This invention relates a wood reinforcing material for strengthening wood material and a reinforced wood material reinforced with the wood reinforcing material.
Heretofore, single wood materials or so-called bonded wood materials formed by bonding sawn woods or small square lumbers cut longitudinally in the direction of fibers with the direction of the fibers being in parallel with each other have been used mainly as frame materials such as post and beams in buildings, as well as for wooden bridges or large scale domes.
Particularly, since the bonded wood materials are assembled from sawn woods and small square lumbers, they have excellent characteristics such as high degree of freedom for the size and dimension, less variation in the strength of products, cracks or errors cause by drying, as well as capable of easily manufacturing bent materials.
However, when such bonded wood materials are used for large buildings and structures, since the rigidity and strength of the bonded materials have to be increased, it is necessary to increase the thickness for the bonded materials and, as a result, this causes problems such as lowering of ceilings in the buildings and structures, or.unnecessary increase in the height of roofs.
Therefore, for providing the bonded wood materials and single wood materials with high rigidity and strength and also providing sufficient water proofness, corrosion resistance, fire resistance, heat resistance and adhesion required for the buildings or structures of woods, it has been proposed to bond carbon fibers by adhesives such as phenolic resins or resorcinolic resins to obtain reinforced wood materials such as carbon fiber-reinforced single wood materials or carbon fiber-reinforced bonded wood materials.
As one of methods for manufacturing such reinforced wood materials, Japanese Laid-Open No. 230904/1991, for instance, discloses a method of coating an adhesive on the surface of wood material, disposing carbon fibers thereon and impregnating an adhesive between the fibers and also bonding the same with the wood material (Prior Art 1).
As another method of manufacturing the carbon fiber-reinforced single wood material or carbon fiber-reinforced bonded wood material, Japanese Patent Laid-Open No. 108182/1978 proposes a method of using a so-called prepreg in which an adhesive is previously impregnated sufficiently to carbon fibers and bonding the same to a wood material (Prior Art 2). This method enables working in various places and is suitable also in view of the fabricability and, accordingly, has been used generally.
The present inventors have proposed a wood reinforcing material by bonding a wood reinforcing carbon fiber prepreg and a wooden sheet in Japanese Patent Laid-Open No. 254319/1997 (Prior Art 3). In this cited invention, release paper is not necessary, the resultant wood reinforcing material has high strength and high rigidity and can obtain high stable properties regarding adhesion performance between the wooden sheet and the wood material, or adhesion performance between the wooden sheet and carbon fibers.
In the Prior Arts 1 and 2, since the wood material is natural products having different natures depending on the growing environments, it involves a problem that adhesion fluctuates when the carbon fiber prepreg and the wood material are bonded. Further, for ensuring the bondability, it requires a frequent control for selecting and optimizing the state such as solid, semi-solid or liquid and amount thereof, which leaves various problems with view point of cost performance and quality.
In the Prior Art 2 described above, since carbon fiber prepregs are generally transported or stored being rolled or stacked into sheets, so that release paper is disposed on one surface or both surfaces of the prepreg. However, when bonding with the wood materials, troublesome and time consuming fabrication operations are necessary such as for removal of the release paper, as well as removed release paper yields wastes and the use of prepregs have resulted in environmental contamination.
In the Prior Art 3 described above, the wooden sheet itself causes shear failure in the bending failure test and sufficient reinforcing effect can not always be obtained.
The present inventors have intended to provide a wood reinforcing material which is applied to wood materials or bonded wood materials for reinforcement capable of overcoming the problems in the prior art, as well as a reinforced wood material in which the wood reinforcing material is applied to the surface of the wood material or to the inner layer of the bonded wood material.
Specifically, this invention intends to provide a wood reinforcing material excellent in bondability with the wood material and handlability, not causing environmental contamination such as forming wastes of release paper, and having a sufficient reinforcing effect for the wood material, as well as reinforced wood material.
More specifically, this invention intends to provide a wood reinforcing material of reducing fluctuation of adhesion performance, strength and rigidity caused by variation in wood materials as natural products and minimizing the complexity in view of the working and minimizing the wastes, as well as having high bondability, strength and rigidity, as well as a reinforced wood material applied with the wood reinforcing material.
It is an object of the present invention to solve the foregoing problems.
In accordance with a wood reinforcing material of this invention, a phenol resin-impregnated sheet with a degree of cure of 70% or more and 95% or less in which a porous sheet is impregnated with a phenol resin is disposed on the surface of a carbon fiber-reinforced thermosetting resin sheet.
Further, in accordance with a reinforced wood material of the invention, the wood reinforcing material is integrated and cured by way of a phenol resin-impregnated sheet on the surface of a wood material.
In the wood reinforcing material of the invention, since a phenolic resin-impregnated sheet with a degree of cure of 70% or more and 95% or less is disposed, it forms a molding product showing excellent adhesion to a wood material to be reinforced and also free from stickiness, so that it does not require release paper. Accordingly, the reinforced wood material according to this invention which is reinforced by applying the wood reinforcing material of the invention to the surface of the wood material has a feature of high strength, high rigidity and high shear strength.
A carbon fiber-reinforced thermosetting resin sheet as a constituent factor of the wood reinforcing material of this invention is reinforced with carbon fiber in the thermosetting resin as reinforcing fibers.
There is no particular restriction on the carbon fibers and carbon fibers obtained from polyacrylonitrile fibers with a nitrogen content of 0.1 to 15% by weight, a tensile strength of 2,500 to 7,000 MPa and a modulus of elasticity of 150-700 GPa are preferred and, particularly, carbon fibers of 5 to 9 mm diameter containing 3 to 10% of a nitrogen content and having 3,500 MPa or more of tensile strength and 200 to 350 GPa of modulus of elasticity are preferred in view of the adhesion.
Further, those in which the oxygen/carbon ratio of 0.01/1 to 0.3/1, particularly, 0.01/1 to 0.25/1 at the surface of the carbon fibers of this invention by an ESCA surface analyzer (manufactured by Shimazu Seisakusho) are preferred since the adhesion strength can be improved.
It is desired that carbon fibers with the fiber diameter of from 5 to 9 mm and fiber strands comprising the fibers by the number of 1,000 to 300,000 are used by being bundled or spread in a sheet-like shape in an amount, with no particular restriction only thereto.
The form of the carbon fiber may be a multi-directional sheet such as woven or non-woven fabrics or linear materials such as uni-directionally oriented sheets or rovings.
Kinds of the thermosetting resins reinforced with carbon fibers have no particular restrictions and, in view of use for buildings, one or more member selected from isocyanate type resins or resorsinol resins, or resol type phenolic resins are preferred, formaldehydes are preferred as the curing agent for the thermosetting resin and inorganic acids or organic acids are preferred for curing catalysts.
Referring more specifically to the thermosetting resins, known resol type phenol resins (phenol formaldehyde initial polycondensation resins) and resorcinol resins obtained by methyloling phenols having a phenol hydroxy group such as phenol, cresol, xylenol, ethylphenol, chlorophenol and bromophenol or phenols having two or more phenolic hydroxy groups such as oligomer, and resorcin, hydroquinone, catechol and fluoroglycinol, and aldehydes such as formaldehyde, para-formaldehyde, acetoaldehyde, fulfural, benzaldehyde, trioxane and tetraoxane, at a molar ratio of phenols/aldehydes=2/1 to 1/3, preferably, 5/4 to 2/5, under the presence of an alkali catalyst such as potassium hydroxide or sodium hydroxide can be used.
More preferably, resins having an average molecular weight as polystyrene of 120 to 2000, and, particularly, 150 to 500 according to high speed liquid chromatography (HPLC) are preferred and those resins having viscosity adjusted to 3 to 150 poise at 25-C are preferred.
Among known curing agents used for resorcinol resins and resol type phenol resins curing agents which become paste or liquid when mixed with the resins such as formaldehyde, acetoaldehyde, furfural or trioxane are preferred.
Curing catalysts which are dissolved into liquid form when mixed with resins such as para-toluene sulfonic acid, benzene sulfonic acid, xylene sulfonic acid and phenol sulfonic acid are preferred.
In view of the production process of the carbon fiber-reinforced thermosetting resin sheets, curing agents or curing catalysts which form homogeneous liquid at 35-C or lower as a temperature for usual production of prepregs when prepared as mixed resins for uniformly curing the prepregs are preferred.
In the fiber reinforcing material of this invention, the carbon fiber-reinforced thermosetting resin sheet as a constituent factor may be a prepreg sheet or a completely cured sheet. It is preferred that the sheet is completely cured with an aim of increasing the strength of the carbon fiber-strengthened resin composite material per se.
The phenol resin impregnated sheet as a constituent factor of the wood reinforcing material of this invention is a sheet formed by impregnating a porous sheet with a phenol resin, for improving the adhesion strength when the wood reinforcing material is bonded by an adhesive on the surface of wood material. Accordingly, it is important that the sheet has thin and uniform thickness.
The thickness of the phenol resin-impregnated sheet is preferably 0.01 mm or more and 1.0 mm or less. If the thickness is less than 0.01 mm, the sheet performance is deteriorated by unevenness caused to the form of the phenol resin-impregnated sheet and, depending on the case, curling in the lateral direction and, in addition, the strength of the sheet is lowered to allow easy tearing by an external force or result in difficulty in the handlability. On the other hand, if the thickness is more than 1.0 mm, the water proofness or shear strength is sometimes lowered.
The porous sheet can include, regarding the form, for example, non-woven fabric, paper and wooden fabric and can include, regarding material, for example, pulp, glass fiber and carbon fiber and synthetic fiber.
The resin impregnating in the phenol resin-impregnated sheet used in this invention is a highly viscous or solid resin such as a phenolic resin or phenol/melamine resin mixture, with no restriction for the presence or absence of the curing agent, and use of a less reactive resin capable of controlling the degree of cure is preferred for attaining the purpose of this invention.
The phenol resin is used because this is excellent in fire proof and heat resistant performance and, further, excellent in water proofness, corrosion resistance and bondability and, thus, this can be used suitably to building materials.
Actual examples of such phenol resins are phenols having one phenolic hydroxy group such as phenol, cresol, xylenol, ethylphenol, chlorophenol and bromophenol or phenols having two or more phenolic hydroxy groups such as oligomer and resorcine, hydroquinone, catechol and fluoroglycinol and, further, resins formed by mixing one or more of resins such as melamine, epoxy, and unsaturated esters with the resins mentioned above.
In the wood reinforcing material of this invention, it is preferred that the degree of cure of the phenol resin in the phenol resin-impregnated sheet as the constituent factor is controlled to 70% or more and 95% or less, preferably, 75% or more and 90% or less, in order to keep favorable adhesion and shear strength. That is, if the degree of the cure of the resin is less than 70%, peeling occurs in the phenol resin-impregnated sheet because of the low degree of the cure of the phenol resin and, on the other hand, if it exceeds 95%, curing proceeds excessively and reactivity with the adhesive is lowered to result in peeling at the boundary with the wood material.
Further, when the degree of cure of the resin in the phenol resin-impregnated sheet is controlled to 70% or more and 95% or less, the wood reinforcing material of this invention forms a molding product with no stickiness thus making it unnecessary for the use of release paper which is indispensable for usual prepregs during storage or transportation.
The degree of cure is measured as follows.
{circle around (1)} For identical phenol resin-impregnated sheets, an uncured phenol resin-impregnated sheet and an optionally cured phenol resin-impregnated sheet are dried each by 100 cm2 in a desiccator containing a silica gel at a normal temperature for 30 min. under a reduced pressure and then further dried in a pressure reduced state for 15 hrs. The weight for the uncured phenol resin-impregnated sheet and the optionally cured phenol resin-impregnated sheet in this case is defined as WO, WOxe2x80x2, respectively.
{circle around (2)} Each of the uncured phenol resin-impregnated sheet and the optionally cured phenol resin-impregnated sheet in above {circle around (1)} is extracted for five hours with the solvent for the phenol resin-impregnated sheet such as acetone using a Soxhlet extractor, dried in a desiccator containing silica gel at a normal temperature for 2 hours under a reduced pressure and, further, dried for 15 hrs in a pressure reduced state. The weight for the uncured phenol resin-impregnated sheet and the optionally cured phenol resin-impregnated sheet in this case is defined as W1, W1xe2x80x2, respectively.
{circle around (3)} Degree of cure is calculated based on and described above {circle around (1)} and {circle around (2)} in accordance with the following equation 1.
Degree of cure (%)=(1xe2x88x92(W0xe2x80x2xe2x88x92S1xe2x80x2)/(W0xe2x88x92W1))xc3x97100xe2x80x83xe2x80x83formula (1)
The carbon fiber-reinforced thermosetting resin sheet and the phenol resin-impregnated sheet can take the following composite structures (1) and (2).
Composite Structure (1):
A composite structure in which the carbon fiber reinforced thermosetting resin sheet and the phenol resin-impregnated sheet are entirely bonded and integrated.
Composite Structure (2):
A composite structure in which the carbon fiber-reinforced thermosetting resin sheet and the phenol resin-impregnated sheet are point-bonded and integrated.
Such composite structures (1) and (2) can be obtained by the following manufacturing method.
Manufacturing Method:
A phenol resin-impregnated sheet is appended on one surface or both surfaces of a so-called prepreg sheet formed by impregnating carbon fibers with a thermosetting resin for wood reinforcement, and then integrating them by using a hot press or the like such that the degree of cure of the phenol resin-impregnated sheet is 70% or more and 95% or less. The thermosetting resin for the carbon fibers in this case may not always be cured completely.
The reinforced wood material in this invention can include single wood materials or bonded wood materials and there are no particular restrictions so long as they are existent wood materials and, usually, wood materials used for building such as cedar, hinoki cypress, larch, Pseudotsuga taxifolia Britt and peel of Citrus aurantium and wood material used for plywoods such as Japanese oak, paulownia, zelkova, maple, horse chestnut, Magnolia obovata Thumb, cherry, teak, lauan and SPINAL can be used.
Wood reinforcing material of this invention (carbon fiber reinforced resin composite material) is used for wood reinforcement as shown below.
The wood reinforcing material of this invention is appended on the surface of a single wood material or to the surface of the single board or any one of board, or between single boards or the surface of a bonded material comprising a plurality of boards or single board and integrated and cured into a reinforced wood material, optionally, with the interposition of adhesives or further necessary, under heating and under pressure.